Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

440
FXUS63 KLOT 252358
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
658 PM CDT Thu Jun 25 2026

.KEY MESSAGES...

- Showers and isolated thunderstorms are expected Friday into
  early Saturday morning, with the highest coverage of showers
  expected south of Interstate 80.

- Another chance for showers and storms Saturday night into
  Sunday morning.

- First heat wave is expected next week for temperatures in the
  90s and peak afternoon heat index values over 100 degrees.

&&

.DISCUSSION...
Issued at 207 PM CDT Thu Jun 25 2026

The Rest of This Afternoon and Early Evening:

Clearer skies today have allowed temperatures to warm up
quickly into the 70s to around 80F this afternoon after the cool
start to the day. While lingering mid level moisture and weak
instability from diurnal heating has allowed for widespread
Cumulus to bubble up, prominent lower to mid-level dry air
supports a dry forecast for the vast majority of the forecast
area. Winds remain out of the northwest with decent mixing
providing occasional gusts to 20 mph this afternoon. However,
winds at Northerly Island have already turned to the northeast,
due to a lake breeze, pretty clearly defined on KLOT and TORD
radars, slowly meandering inland. The exception to the previous
shower forecast would be areas along the lake breeze this
afternoon, with the best chance for an isolated shower in Lake
County Illinois and farther north into southeastern Wisconsin.

Tonight Onward:

Models are still showing decent spread in the track of the next
upper level impulse with a subsequent surface low that will
pass over central Illinois late tonight through tomorrow.
However, the consensus was showing a northeastward movement of
the low just south of Ford, Iroquois and Benton counties, which
justified dragging slight chance PoPs as far north as the
Wisconsin stateline. That being said, the higher confidence in
shower coverage remains closer to the low, and therefore along
and south of Interstate 80. Lapse rates do not look particularly
steep. Perhaps there will be isolated embedded storms, but
confidence is lower on the thunder threat. Model soundings are
showing a fairly moist air mass with precipitable water amounts
approaching two inches for areas along the US-24 corridor. While
the higher concentration of total QPF is still expected in
central Illinois, there is a chance that efficient rain
processes could create instantaneous rates in excess of an inch
per hour tomorrow afternoon and evening. Downpours are possible
south of Interstate 80, with better chances of any localized
flooding concerns farther south around US-24, which is an area
that has fairly saturated soils from recent rains.

Guidance has also slowed the progression of the wave eastward.
Showers may linger into Saturday morning, but overall drier
conditions are expected through the rest of the day. An upper
level high centered over Louisiana will quickly amplify
northward through the weekend. As an upper level low spins over
the Rockies, a mid level wave is projected to eject out and
follow a northeastward trajectory between the high and low
Saturday night into Sunday morning. If a weaker solution for the
ridging (and associated capping) materializes, there could be
an increase in PoPs needed. However, there is currently decent
agreement that the higher PoPs look to remain west of Interstate
55 for another chance of showers and thunderstorms overnight
and slowly diminishing Sunday morning.

As conditions dry out on Sunday, winds will turn to the
southwest and advect in a warmer air mass. The upper level high
is expected to deepen through the early part of the week and sit
near the Ohio River Valley temperatures are expected to climb
into the 80s on Sunday and 90s through the middle of the week.
Dew points are forecasted into the 70s which will create a humid
air mass that will feature heat index values into the 100s. The
main uncertainty with temperatures right now will depend on
where the core of the upper level high actually is located. If
it were to establish itself a little farther south, there may
be a disturbance or two that passes through the upper level
pattern, yielding a few periods of some showers and storms to
break the grip on the heat. But for now, confidence is low and
will continue to be watched. Aside from the lower end/lower
confidence convective potential, next week`s heat and humidity
looks to be the first formidable stretch of potentially
dangerous heat this summer.

DK

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 658 PM CDT Thu Jun 25 2026

Key aviation forecast messages:

- NE wind shift behind lake breeze/backdoor front this evening

- Potential for a period of rain on Friday with greatest
  coverage near/south of I-80

A lake breeze is beginning to make inroads toward ORD after
having stalled east of the terminal all afternoon with a
slightly slower westward progression occurring near MDW. Have
adjusted the northeast wind shift to 00:15 to reach ORD and
00:30 at MDW based on the latest trends. Meanwhile a backdoor
front diving down Lake Michigan recently reached UGN where the
initial wind shift was around 11-12kt before easing closer to
8kt after 30 mins or so. Expect something similar at area
terminals as the combined lake breeze/front move through. Have
added more detail for the wind shifts at DPA and RFD as well
before winds eventually ease late in the evening and overnight.
Winds then remain generally east to northeast through the end of
the period, increasing back to around 10 kt after daybreak on
Friday.

A disturbance is expected to drift across central Illinois and
Indiana on Friday bringing rain to at least portions of the
area mid-morning through early evening. At this time confidence
in rainfall is highest near and south of Interstate 80, with
lower confidence on the northward extent. In addition to
shifting the PROB30s to begin a bit earlier (closer to 16Z),
have accordingly trended them slightly less pessimistic for MDW
(high-end MVFR) and even moreso for ORD (remaining VFR). The
potential for prevailing showers is highest at GYY (50% chance).

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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